/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.aop.aspectj.annotation;

import java.io.Serializable;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Decorator to cause a {@link MetadataAwareAspectInstanceFactory} to instantiate only once.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 2.0
 */
@SuppressWarnings("serial")
public class LazySingletonAspectInstanceFactoryDecorator implements MetadataAwareAspectInstanceFactory, Serializable {

    private final MetadataAwareAspectInstanceFactory maaif;

    @Nullable
    private volatile Object materialized;


    /**
     * Create a new lazily initializing decorator for the given AspectInstanceFactory.
     *
     * @param maaif the MetadataAwareAspectInstanceFactory to decorate
     */
    public LazySingletonAspectInstanceFactoryDecorator(MetadataAwareAspectInstanceFactory maaif) {
        Assert.notNull(maaif, "AspectInstanceFactory must not be null");
        this.maaif = maaif;
    }


    @Override
    public Object getAspectInstance() {
        Object aspectInstance = this.materialized;
        if (aspectInstance == null) {
            Object mutex = this.maaif.getAspectCreationMutex();
            if (mutex == null) {
                aspectInstance = this.maaif.getAspectInstance();
                this.materialized = aspectInstance;
            } else {
                synchronized (mutex) {
                    aspectInstance = this.materialized;
                    if (aspectInstance == null) {
                        aspectInstance = this.maaif.getAspectInstance();
                        this.materialized = aspectInstance;
                    }
                }
            }
        }
        return aspectInstance;
    }

    public boolean isMaterialized() {
        return (this.materialized != null);
    }

    @Override
    @Nullable
    public ClassLoader getAspectClassLoader() {
        return this.maaif.getAspectClassLoader();
    }

    @Override
    public AspectMetadata getAspectMetadata() {
        return this.maaif.getAspectMetadata();
    }

    @Override
    @Nullable
    public Object getAspectCreationMutex() {
        return this.maaif.getAspectCreationMutex();
    }

    @Override
    public int getOrder() {
        return this.maaif.getOrder();
    }


    @Override
    public String toString() {
        return "LazySingletonAspectInstanceFactoryDecorator: decorating " + this.maaif;
    }

}
